Until recently, wireless mobile terminals have been used basically for making voice calls. Standardised and well-established communication technologies and protocols are then utilised to communicate voice between fixed and/or mobile terminals using circuit-switched communication channels. However, a multitude of new multimedia telephony services are now rapidly being developed, enabled by the introduction of new technologies allowing for notably higher transmission rates and increased network capacity. For example, GPRS (General Packet Radio Service) and WCDMA (Wideband Code Division Multiple Access) technologies are currently emerging for enabling wireless telephony services requiring a wide range of transmission rates and different protocols and media formats.
Further, new sophisticated mobile terminals are also emerging on the market, equipped with functionality to handle the new services, including high resolution colour displays and various codecs (coders/decoders) e.g. for handling visual information.
The trend today in the field of telecommunication is a move towards packet-switched networks and technologies using the packet-based Internet Protocol (IP), providing more capacity and flexibility as compared to the traditional circuit-switched networks. Recently, a network architecture called “IP Multimedia Subsystem” (IMS) has therefore been developed by the 3rd Generation Partnership Project (3GPP) as an open standard, to give operators of access networks the ability to offer multimedia services in the packet domain. IMS is a platform for enabling services based on IP transport, more or less independent of the access technology used, which is basically not restricted to any limited set of specific services.
Multimedia services typically involve the transmission of different types of content such as text, documents, images, video and audio files or “clips” in various formats and combinations. The term “multimedia” will be used in this description to represent telephony services requiring the transfer of any choice of content, in addition to ordinary voice. Multimedia communication sessions typically involve combinational services with voice and other media at the same time.
It has been proposed that a multimedia session should be divided into a circuit-switched (CS) part for the voice transport, and a packet-switched (PS) part for the transport of other data in combinational services. In this way, the high performance associated with circuit-switching is obtained for voice, whereas not equally delay-sensitive multimedia content can be adequately transferred by packet-switching. New access networks typically allow for simultaneous CS and PS communication, such as WCDMA networks and GSM networks having DTM (Double Transfer Mode) capability.
During a session between two terminals, certain session parameters defining the rules of communication must be used by both terminals in order to send and receive any desired information. Such session parameters may be related to available codecs, applications and multiplexing schemes. Two communicating terminals may have different capabilities with respect to the above, and each terminal has initially no knowledge of the capabilities of the other. Hence, in order to establish a multimedia session, session parameters that both terminals can handle must therefore first be selected and determined by exchanging capabilities.
A specification for session setup has been defined called “SIP” (Session Initiation Protocol, according to the standard IETF RFC 3261 et al). SIP is an application-layer control (signalling) protocol for creating, modifying and terminating sessions over a packet-switched logic. In SIP, a method called “INVITE” is defined to initiate a session during a setup procedure when the terminals basically exchange their capabilities.
Another method called “OPTIONS” is also specified in the SIP protocol allowing one terminal to query another terminal as to its capabilities regarding codecs and supported applications, without the user actually “calling” the other party. According to this method, the terminal sends a capability query called “SIP OPTIONS”, preferably includes its own capabilities, to the other terminal which then responds by sending over its capabilities. A “SIP OPTIONS update” message can also be sent if they are changed. In this way, both terminals will become aware of each other's capabilities. The OPTIONS method can also be used during an ongoing voice call for enriching the call with multimedia, provided that both access networks allow for packet-switched communication in addition to the currently ongoing circuit-switched communication.
By having knowledge of the other terminal's capabilities, each terminal can determine which multimedia service and/or application options that are available to their users, hereafter called “multimedia options” for short, based on their mutual capabilities. A highly desirable feature is that terminal users should be able to see on the terminal screen which multimedia options are currently available. Thus, after exchanging capabilities each terminal may indicate the available multimedia options to their users on the terminal screen. Most commonly, associated icons are then displayed but any other indication means may be used as well, such as other symbols, codes, texts, menu lists, etc. In this way, a user can easily select which type of service and media to use in a multimedia session with the other party.
For example, a multimedia option may be indicated as being available by the mere presence of an associated symbol, icon, text or list entry on the terminal screen, or by highlighting a displayed option by means of a specific colour, light intensity, size, etc. An unavailable option may be indicated by having a different colour, e.g. grey, light intensity or size, or by being crossed-over, or simply by being deleted from the screen. Thus, it is clearly understood that the availability and non-availability of multimedia options can be indicated in many different ways, and the present invention is not limited in this respect. In this description, the term “option indication” will represent any possible manner of indication.
When two terminals are engaged in a simple CS voice call, one of them (or both) may currently experience access constraints, such that a PS connection is not admitted in addition to the ongoing CS call depending on limitations in the access network. For example, a standard GSM network cannot handle PS connections and CS connections at the same time, although it may admit a PS connection separately. Some networks, including older GSM networks, may lack PS capability altogether admitting CS connections only. Further, one and the same network may comprise certain geographic coverage areas admitting multimedia communication, e.g. specific non-constrained cells, and also other coverage areas not admitting multimedia communication, e.g. constrained cells.
Modern terminals typically have the dual capability of executing a PS session simultaneously with a CS call in order to provide combinational services. Furthermore, there are known mechanisms for a terminal to change its radio access during an ongoing call, e.g. by moving from one coverage area into another one. For example, some terminals are capable of both GSM access and WCDMA access by having dual radio parts.
Two terminals A and B may initially be prevented from establishing a multimedia session, due to access constraints for at least one terminal A having dual access capability. Terminal A may later, during the ongoing call, obtain a new access allowing for an added PS part, e.g. by changing from a standard GSM access to a WCDMA access or to a GSM/DTM access. When moving in the opposite direction, the terminals will experience disablement of previously available multimedia options. Thus, when a communicating mobile terminal move between different types of access networks, the prerequisites for multimedia communication may consequently change. This is a fact even if the other terminal is connected to an access network allowing for multimedia communication with simultaneous CS and PS connections.
The International Patent Application PCT/SE2004/001671, filed Nov. 15, 2004, discloses a solution for enabling multimedia communication during an ongoing circuit-switched call. First, a mobile terminal uses an access having constraints by not admitting simultaneous PS and CS communication. A change of connection is detected to another access admitting simultaneous PS and CS communication, and the terminals exchange capabilities in response to the connection change. Then, possible multimedia options may be indicated to the users, e.g. on the terminal screens.
If the feature of displaying available multimedia options on terminal screens is used in at least one of two communicating terminals, it is a problem that the displayed options may become irrelevant as soon as any change of access occurs for either of the terminals, due to constraints in the new access. Thus, it is desirable to increase the accuracy of this feature.